Embankments Through Cross River Swamp

The design, construction and performance of embankments across a deep clay flood plain are described, the construction involving a two-stage procedure with sand drains to aid consolidation. The Cross River was the major phisical obstacle to the roadlink between Calabar and the mainland of Nigeria constructed between 1975 and 1977. The paper describes the investigation, alignment selection, design, construction and performance of embankments across the Cross River flood plain (Swanp), consisting of clays up to 30m deep. A two-stage construction procedure was employed, with sand hydraulically pumped up to 5km as embankment material. Sand drains were used for radial drainage and as relief wells to speed the consolidation and strengthening of the upper levels of the clay, prior to final embankment construction. Foundation performance was evaluated and strength increases measured. The embankments are performing satisfactorily, but they experienced large initial settlements during construction.